In recent years, a significant industry has developed which involves the application of customer-selected designs, messages, illustrations, and the like (referred to collectively hereinafter as “images”) on articles, such as T shirts, sweat shirts, leather goods, and the like. These images may be commercially available products tailored for a specific end-use and printed on a release or transfer paper, or the customer may generate the images on a heat transfer paper. The images are transferred to the article by means of heat and pressure, after which the release or transfer paper is removed. Generally, unless special inks are employed, images transferred to porous substrates, such as fabrics and leather, are supplemented with a transfer coating (transferable surface) which transfers with the inks, toners or other colorants. Such coatings are necessary or helpful to carry the image colorants into the porous substrates. Also, such coatings are necessary or helpful to adhere the colorants to the substrates and act as protection against wear.
Heat transfer papers having an enhanced receptivity for images made by wax-based crayons, thermal printer ribbons, ink-jet printers, laser-jet printers, and impact ribbon or dot-matrix printers, are well known in the art. Typically, a heat transfer material includes a cellulosic base sheet and an image-receptive coating on a surface of the base sheet. The image-receptive coating usually contains one or more film-forming polymeric binders, as well as, other additives to improve the transferability and printability of the coating. Other heat transfer materials include a cellulosic base sheet and an image-receptive coating, wherein the image-receptive coating is formed by melt extrusion or by laminating a film to the base sheet. The surface of the coating or film may then be roughened by, for example, passing the coated base sheet through an embossing roll.
Much effort has been directed at generally improving the transferability of an image-bearing laminate (coating) to a substrate. For example, an improved cold-peelable heat transfer material has been described in U.S. Pat. No. 5,798,179, which allows removal of the base sheet immediately after transfer of the image-bearing laminate (“hot peelable heat transfer material”) or some time thereafter when the laminate has cooled (“cold peelable heat transfer material”). Moreover, additional effort has been directed to improving the crack resistance and washability of the transferred laminate. The transferred laminate must be able to withstand multiple wash cycles and normal “wear and tear” without cracking or fading.
Various techniques have been used in an attempt to improve the overall quality of the transferred laminate and the article containing the same. For example, plasticizers and coating additives have been added to coatings of heat transfer materials to improve the crack resistance and washability of image-bearing laminates on articles of clothing. Generally, it is possible to design such papers for use with specific substrates. For example, a heavier transfer coating is needed for a coarse, heavy fabric such as a sweatshirt fabric than for light fabrics such as silk or less porous substrates such as leather.
Heat transfer papers generally are sold in standard printer paper sizes, for example, 8.5 inches by 11 inches. Graphic images are produced on the transferable surface or coating of the heat transfer paper by any of a variety of means, for example, by ink-jet printer, laser-color copier, other toner-based printers and copiers, and so forth. The image and the transferable surface are then transferred to a substrate such as, for example, a cotton T-shirt. In most instances, transfer of the transfer coating to areas of the articles which have no image is necessary due to the nature of the papers and processes employed, but it is not helpful or desirable. This is because the transfer coatings can stiffen the substrates, make them less porous and make them less able to absorb moisture.
Thus, it is desirable that the transferable surface only transfer in those areas where there is a graphic image, reducing the overall area of the substrate that is coated with the transferable coating. Some papers have been developed that are “weedable”, that is, portions of the transferable coating can be removed from the heat transfer paper prior to the transfer to the substrate. Weeding involves cutting around the printed areas and removing the coating from the extraneous non-printed areas. However, such weeding processes can be difficult to perform, especially around intricate graphic designs.
Therefore, there remains a need in the art for improved weedable heat transfer papers and methods of application. Desirably, the papers and methods provide good image appearance and durability.